Build: v1.6.0 Build 15262.2076517 (modded)
First and foremost, I know the "Guide to posting in Multiplayer" thread requests to include the save games from the host and client. However, those elements will not be needed for this report.
My brother and I have tested this issue thoroughly. With no mods activated (build still says modded even though none were active because we're still subscribed), our brand new multiplayer game desyncs once both of us finish our turn on turn 1 (as it speeds through the rest of the AI factions) without fail and no matter which faction we choose to play as. It is impossible to resync. This issue only occurs on versions 1.6.0 and 1.6.1 (the beta patch). When rolling back to 1.5.3 (and with The Furious Wild and Shi Xie DLCs disabled), multiplayer works fine. This has led us to believe that multiplayer has been broken upon the latest release.
I'm not sure if this issue is occurring for everyone or just me and my brother. I have heard on the Total War discord though that others have experienced an increased amount of desyncs with these latest releases. This seems like something that should have been caught by a QA process and it's a bit disappointing that my brother and I have paid for a new DLC but are unable to play it together.